1. Field of the Invention
The present invention relates to a magnetoresistive element (magnetoresistance-effect element) providing a tunnel effect, which can be used as a component element of a magnetic device that is expected to have a high magnetic field sensitivity even for a low magnetic field, and also relates to a magnetic memory and a magnetic head, each of which uses the foregoing element.
2. Related Background Art
Magnetic sensors, memory elements, magnetic heads, etc. have been proposed as solid devices using magnetoresistive (MR) films. Studies so far made have proven that the MR effect a giant-magnetoresistive (GMR) film exhibits in response to a current flow perpendicular to a plane of the film (CPPMR) is greater than the MR effect the film exhibits in response to in-plane current flow (CIPMR). Further, a tunneling GMR (TMR) film with a high impedance can be expected to provide a further greater output.
Recently, a manganese (Mn) oxide having a perovskite structure has been reported as a material with a high magnetic polarizability (Y. Lu et al.: Phys. Rev. Lett. 54(1996)R8357).
To form a TMR film using such an oxide, compatibility between materials laminated is particularly significant. This is because characteristics of a TMR film depend considerably on a degree of discontinuity at a barrier layer interface. In the case where a complex oxide such as a perovskite Mn oxide is used, particularly, it is difficult to secure the discontinuity at the barrier layer interface.
Therefore, with the foregoing in mind, it is an object of the present invention to obtain excellent tunnel junction with use of the perovskite-type oxide, so as to provide a practical magnetoresistive element that exhibits a great magnetoresistance effect even in response to a low magnetic field. Further, it also is an object of the present invention to provide a device in which the foregoing element is used.
A magnetoresistive element of the present invention includes a layered-perovskite oxide (an oxide having a layered perovskite structure) having a composition expressed by a formula L2(A1xe2x88x92zRz)2Anxe2x88x921MnO3n+3+x and including a (L-O)2 layer in its crystalline structure, and a pair of ferromagnetic bodies formed in contact with the perovskite oxide layer so as to sandwich the oxide. In this element, a magnetoresistive tunnel effect appears in response to bias application via the (L-O)2 layer.
Herein, A represents at least one alkaline earth element selected from the group consisting of calcium (Ca), strontium (Sr), and barium (Ba), L represents at least one element selected from the group consisting of bismuth (Bi), thallium (Tl), and lead (Pb), M represents at least one element selected from the group consisting of titanium (Ti), vanadium (V), copper (Cu), ruthenium (Ru), nickel (Ni), manganese (Mn), cobalt (Co), iron (Fe), and chromium (Cr), R represents a rare earth element (preferably at least one element selected from the group consisting of lanthanum (La), praseodymium (Pr), neodymium (Nd), and samarium (Sm)), n is 1, 2, or 3, and x and z are numerical values satisfying xe2x88x921xe2x89xa6xxe2x89xa61, and preferably 0xe2x89xa6z less than 1, respectively.
The above-described layered-perovskite oxide includes a (L-O)2 barrier layer that per se includes a magnetoresistive tunnel junction array. In the present invention, a ferromagnetic body is further provided in contact with the foregoing oxide, so as to make the element more practical with view to application to various devices.
As will be described below, in one embodiment of the present invention, at least one of the ferromagnetic bodies is made of a perovskite oxide, and an oxide electrode is attached to this complex oxide ferromagnetic body. By so doing, excellent junction can be obtained as a whole. Further, in another embodiment of the present invention, one of the ferromagnetic bodies is made of a perovskite oxide, and the other is made of a metallic ferromagnetic material. Furthermore, in still another embodiment of the present invention, an antiferromagnetic body is provided in contact with one of the ferromagnetic bodies.
Thus, in the present invention, the foregoing layered-perovskite oxide is utilized, thereby allowing discontinuity to be obtained at the barrier layer interface. Further, a ferromagnetic body, an antiferromagnetic body, an oxide electrode, etc., compatible with the foregoing oxide are arranged additionally as required. By so doing, it is possible to provide a highly sensitive magnetoresistive element that is applied suitably in various devices (for instance, a magnetic head and a magnetic memory element).